Concrete products can be produced without any coloring agents, in which case the resulting product will have a color dictated by the native colors of the raw materials, typically cement and aggregate, that have been used. The result is typically a shade of gray. It is possible to alter this gray color by introducing a coloring agent into the mixture. The coloring agent is typically a pigment, or a mixture of pigments, that will impart the desired color to the finished product.
There are a variety of known processes for making concrete products. In a wet cast system, a concrete mixture that contains sufficient water so that it flows readily is introduced into a closed mold. The mixture is allowed to harden in the mold, and the molded product is then stripped from the mold. In a dry cast system, a much drier concrete mixture is introduced into a mold. The concrete mixture is densified in the mold, and then removed from the mold before it has hardened. Because the concrete mixture is of a “low slump” or “no slump” nature, the molded product, if carefully handled, will retain its molded shape while it is transported to a curing area, where it will cure over a period of hours. This dry cast process is suitable for highly automated, mass production of a number of types of concrete products, including architectural concrete blocks, segmental retaining wall units, concrete bricks, slabs, and interlocking concrete pavers.
In recent years, it has become desirable to produce some of these products with variegated colors, rather than with uniform colors. The variegated color products will have two or more distinct colors visible in the finished product, with the colors folded, or swirled, or mottled in some fashion. This is a popular look in landscape products in particular, where the appearance of naturally-occurring, variegated colored stone is being sought. In this specification, the term “color blended” will be used to refer to such a variegated color appearance.
An example of a known dry cast concrete product production system 5 is illustrated in FIG. 1. The system 5 includes a mixer 6 in which a batch of the low slump concrete is mixed from known components. After mixing, the batch of uncured concrete is transported by a conveyor 7 to a surge hopper 8, with the concrete being deposited into the hopper 8. Uncured concrete is then metered from the hopper 8 onto a metering belt 9 which transports the metered amount of concrete to a production machine 10 which forms a plurality of concrete products from the concrete.
The production machine 10 includes a hopper 15 that receives the concrete from the metering belt 9. The production machine 10, as would be understood by a person having ordinary skill in the art, includes molds that are open at the top and bottom. A pallet is positioned below each mold to close the bottom of the mold, and the uncured concrete is delivered from the hopper 15 into each mold through the open top of the mold via one or more feed drawers. The uncured concrete is then densified and compacted by a combination of vibration and pressure. The mold is then stripped by a relative vertical movement of the mold and the pallet to remove the uncured concrete product from the mold. The uncured product is then transported to a location where it is cured. The production machinery needed to construct a system of this type is available from Besser Company of Alpena, Mich., as well as from a number of other sources, including Columbia Machine Company, Tiger Machine Company, Masa, Omag, Rikers, Hess, KVM, Zenith, and others. Batching and mixing equipment is available from a number of sources well known in the industry. Color pigments are available from a number of sources, including Bayer, Davis Color, and Hamburger Color Company.
Returning to FIG. 1, color blending has previously been achieved by preparing a batch of concrete of a first color and depositing a first colored concrete layer 11 in the hopper 8, preparing a batch of concrete of a second color and depositing a second colored concrete layer 12 in hopper 8 on top of the first layer of concrete 11, and, if a third color is desired, preparing a batch of concrete of a third color and depositing a third colored concrete layer 13 in hopper 8 on top of the second layer 12. For example, the first layer 11 can be black concrete, the second layer 12 can be brown concrete, and the third layer 13 can be gray concrete. Blending of the three colors occurs within the hopper 8, as the concrete is metered from the hopper 8 onto the metering belt 9, on the metering belt 9 itself, and within the production machine 10 prior to being introduced into the molds.
A difficulty with this previous blending process is that the blending of the different colors, and the resulting color blended look of the concrete product, are not controllable. The initial amount of concrete that is metered from the hopper 8 onto the belt 9 is mostly a single color from the layer 11. Therefore, concrete products made from the initial amount of concrete will have little or no color blending, and as a result, will have an appearance that is significantly different from concrete products that are formed from later metered amounts of concrete. These initial products are often discarded due to insufficient blending. In addition, the final amount of concrete from the hopper 8 is often primarily a single color from the layer 13, so that products made from this final amount are also frequently discarded.
Further, the color blending that does occur in the hopper 8 and downstream from the hopper is random, as is the amount of each color contained in the concrete that is metered from the hopper 8 onto the belt 9. Therefore, products produced from one metered amount of concrete may have one look, while products produced from another metered amount of concrete may have an entirely different look. This can be a problem when it is desired to achieve a somewhat consistent color blended appearance.
In addition, the design of the hopper 8 is such that the entire amount of concrete must be used up before new color layers 11-13 can be introduced. Therefore, if the decision is made to change the blended look of the products while concrete remains in the hopper 8, it is generally necessary to use up the remaining concrete in the hopper, or discard the remaining concrete entirely. The need to use up all of the concrete in the hopper 8 also slows down production, since the mixer 6 must then form each new colored batch for introduction into the hopper 8. While the hopper is being refilled, the production machine 10 may be standing idle waiting for filling to be complete and for new concrete to be metered from the hopper.
Moreover, due to the relatively long time the colors are in contact with each other, the colors can bleed together and produce areas on the resulting products having a color that is a mixture of two or more colors. This bleeding of colors can detract from the appearance of the product, by blurring the colors at the junctures between colors, which blurs the separation between colors in the resulting product.
Accordingly, there is a need for an improved process and equipment for producing color blended concrete products, in which there is more control of the resulting color blended appearance of the products, so that the appearance is generally repeatable, and at the same time reducing the amount of waste and reducing production down time.